Optical Imaging Writer System

ABSTRACT

System and method for applying mask data patterns to substrate in a lithography manufacturing process are disclosed. In one embodiment, a parallel imaging writer system comprises a plurality of spatial light modulator (SLM) imaging units, and a controller configured to control the plurality of SLM imaging units. Each of the plurality of SLM imaging units includes one or more illumination sources, one or more alignment sources, one or more projection lenses, and a plurality of micro mirrors configured to project light from the one or more illumination sources to the corresponding one or more projection lens. The controller synchronizes movements of the plurality of SLM imaging units with movement of a substrate in writing a mask data to the substrate in a lithography manufacturing process.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. non-provisionalpatent application Ser. No. 12/475,114, “An Optical Imaging WriterSystem” filed May 29, 2009, which is a continuation-in-part of, andclaims priority under 35 U.S.C. §120 to U.S. non-provisional patentapplication bearing Ser. No. 12/337,504, filed Dec. 17, 2008, whichclaims the benefit of U.S. provisional application No. 61/099,495, “AnOptical Imaging Writer System” filed Sep. 23, 2008. U.S. non-provisionalpatent application Ser. No. 12/475,114 also claims the benefit ofprovisional application bearing Ser. No. 61/162,286, filed Mar. 21,2009. The aforementioned United States applications are herebyincorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to the field of lithography formanufacturing. In particular, the present invention relates to systemand method for applying mask data patterns to substrate in a lithographymanufacturing process.

BACKGROUND OF THE INVENTION

Fast-paced technology progress in semiconductor integrated circuit (IC)industry has benefited well for the manufacturing of active matrixliquid crystal display (AMLCD) TV and computer monitor displays. In therecent years, the size of LCD TV and computer monitor displays has grownto be larger and yet more affordable.

In the semiconductor IC industry, a technology generation is defined bythe critical dimension (CD) of the circuit design rules. As eachtechnology generation progresses, the IC of the later generation hassmaller feature CD target and tighter tolerance. For the Flat PanelDisplay (FPD) industry, on the other hand, a technology generation isclassified by the physical dimension of substrate used in manufacturing.In one example, the substrate sizes (in millimeter×millimeter) of FPDssixth generation (G6) in 2005, eighth generation (G8) in 2007, and tenthgeneration (G10) in 2009 are 1500×1800, 2160×2460, and 2880×3080respectively.

The lithography challenges in terms of making semiconductor ICs and FPDsubstrates are both trying to make larger sizes more affordable.However, they are entirely different from the manufacturing perspective.For the IC industry, a primary challenge is small CD features can beproduced on a round 300 mm wafer. The goal is to pack as manytransistors as possible for achieving better functionalities in the samedie size. But for the FPD industry, one primary challenge is how largean entire rectangle substrate can be processed. The larger FPD substratecan be processed in a manufacturing line, the bigger size TVs ormonitors can be produced with lower cost. The typical LCD TVs andmonitors are designed with more sophisticated thin film transistor (TFT)for better performance. Still, the TFT CD target remains in the samespecification range. In one viewpoint, one of the main challenges forFPD manufacturing is to keep throughput in pace with justifiableeconomics for each successive generation. Achieving profitable processyield is a key consideration, and the manufacturing process window needsto be preserved.

Conventionally, lithography technologies for manufacturing of FPD arederived from lithography process technologies for making semiconductorICs. Majority of lithography exposure tools used for making FPDsubstrates are projection stepper and/or scanner systems. These areeither 2-times reduction or 1-to-1 projection from mask to substrate. Inorder to project mask patterns to the substrate, the mask must first bemade with the acceptable CD specifications. The FPD mask manufacturingprocess is similar to the one used for manufacturing semiconductor ICs,with the exception that the mask size for making semiconductor ICs isabout 150 mm or 6 inches per side, whereas the mask size formanufacturing FPD, in one example, may be nearly 8-times larger perside, or physically more than one meter per side.

FIG. 1 illustrates a conventional configuration of projection exposuretool used for scanning mask patterns onto FPD substrate. In thisconfiguration, the exposure sources used are mainly high pressuremercury (Hg) short-arc lamps. The incoming illumination light isreflected by a light folding minor 102, and the reflected light passesthrough a mask 104, a projection lens 106 before it reaches a FPDsubstrate 108. The concern of using this conventional mask-basedexposure tool configuration as shown in FIG. 1 for the upcoming FPDlithography manufacturing is the issue of handling the increasingphysical size of masks. In one example, for the G8 FPD, the size of amask is about 1080 mm×1230 mm. The area size of G8 substrate is fourtimes larger. The TFT CD feature specification is in the range of 3microns ±10%. The CD control for TFT over more-than-two-meters per sideof G8 substrate is more challenging than controlling specifications forprinting advanced IC features on a 300 mm silicon wafer. The challengefacing the FPD industry is to build such a mask-based exposure tool costeffectively for the upcoming FPD generations while preserving acceptablelithography process window.

To mitigate CD uniformity issue over the entire FPD exposure field, oneapproach is to use multiple exposures method. The nominal exposure iscomposed of several component exposures in adequate proportions. Eachcomponent exposure uses pre-selected wavelength for illumination alongwith the corresponding projection lens for scanning and stepping. Morethan one projection lenses need to be included in this type of exposuretool but only single illumination source is equipped. This is due to theneed of using high powered Hg short-arc illumination sources in kiloWatts (KW) for throughput. The selection of exposure wavelength can bedone by applying adequate filter to the source. In one example, thismulti-wavelength exposure method relaxes the negative impact on CDuniformity over a G8 substrate hence allowing more economical quality oflens and illumination set-up to be used.

In using multi-wavelength exposures, it is necessary to specify morestringent CD target and uniformity on the mask itself. In one example,the TFT mask CD tolerance is under 100 nm, much smaller than otherwisenecessary for the nominal 3 microns mask CD target. One reason is thatthe process window for FPD lithography manufacturing can be moremanageable for the existing exposure tool configuration. Unfortunately,the tighter FPD mask CD specifications required would push the alreadycostly mask set to be even more expensive. In some situations, making acritical level mask for the G8 FPD becomes very expensive and has longdelivery lead time.

Yet another problem with the conventional approach is the defect densitycontrol for the use of larger sized masks. Lithography processing withsuch a large size mask using multiple exposures, even starting withdefect free mask, is prone to introduce detrimental defects. A defectprone process impacts yield and ultimately the cost of the mask.

FIG. 2 illustrates a conventional mask making exposure toolconfiguration. In this exposure tool configuration, illumination light202 is sent to a beam splitter 204 and then partially reflected toilluminate the spatial light modulator (SLM) 206 through a Fourier lens208. Then, the imaging light rays reflected back, pass through theFourier lens 208, the beam splitter 204, the Fourier filter 210 and thereduction lens 212, and finally reach to the mask blank substrate 216.Mask data 214 is sent to the SLM 206 electronically to set themicro-mirror pixels. The reflected light produce bright spots on themask blank substrate 216, or otherwise absence of reflected light wouldproduce dark spots on the mask blank substrate 216. By controlling andcomposing the reflections, mask data patterns can be transferred to themask blank substrate 216.

Note that for this type of exposure tool configuration, the illuminationlight path is folded in order to illuminate the SLM at a right angleincidence. This folded illumination path makes a “T” joint to theexposure imaging path. In addition to high power illumination source,this type of exposure system requires using projection lens with highreduction ratio in order to write mask pattern in high accuracy andprecision. Typically, the lens reduction ratio is about 100 times. Usingsuch a high reduction ratio of lens makes the exposure field very smallwith a single SLM die. The physical die size for SLM is in theneighborhood of 1 cm. After a 100-times reduction, the SLM writing fieldis reduced to around 100 microns. This writing field size is very smalland therefore slow when attempting to write a full G8 FPD mask.

Another conventional approach is to use multiple laser beams toilluminate the SLM in succession. The multiple beams are generated byreflecting a single illumination laser source from multi-faced rotatingminors. Multiple illumination beams speed up mask writing as they makemultiple exposures at a given time. With this configuration, in oneinstance, the time for writing a G8 FPD mask takes nearly twenty hours.Such a long write time makes machine control expensive to sustain bothmechanically and electronically, hence increases the cost of the FPDmask produced. Using the same exposure tool for the upcoming G10 orbeyond, the cost of manufacturing FPD masks will be even higher.

In another conventional approach, to address the mask cost issue for lowvolume prototyping application, one exposure tool configuration is tomake use of transparent SLM as the mask. This is done such that the maskpattern can be read into SLM to show desired mask patterns without theneed to make a real physical mask. The function of such a transparentSLM mask takes place of the real mask. This saves the mask cost. Fromthe exposure tool configuration perspective, this method is essentiallythe same as the mask-based projection system. Unfortunately, the SLMmask has lower image quality as compared to the image quality on anactual mask. It does not meet the pattern specification requirements forFPD manufacturing.

In yet another conventional approach, a process for roll-to-rollmanufacture of a display by synchronized photolithographic exposure on asubstrate web is described in U.S. Pat. No. 6,906,779 (the '779 patent).The '779 patent teaches a method to expose mask pattern on a roll ofsubstrate. In addition, another conventional method for doingroll-to-roll lithography is described in the article “High-SpeedRoll-to-Toll Nanoimprint Lithography on Flexible Plastic Substrates” bySe Hyun Ahn, etc., Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim; AdvancedMaterials 2008, 20, page 2044-2049 (the Ahn article).

However, in both conventional methods described above, the mask islimited to a predetermined physical size, and the physical maskdimension essentially limits the dimension of the flexible display thatcan be manufactured. Another problem with the conventional methodsdescribed by the 779 patent and the Ahn article is that, to achieve areasonable printing result, the roll of substrate must be stretched flatduring the exposure stage. As a result, the surface flatness of thesubstrate is not as good as rigid glass substrate, typically used forLCD TV display. With such a mask-based lithography, the depth of focus(DOF) is limited due to uneven substrate surface. Thus, it can be verychallenging for these conventional methods to pattern TFT featurecritical dimension (CD) at 5 μm or less. To achieve decent definitiondisplay based on TFT, it is necessary to have CD for TFT mask pattern inthe neighborhood of 3 μm.

The challenges discussed previously for the manufacturing of futuregenerations of FPDs are driven by the need for cost reduction for theFPD industry. One key motivation is to achieve cost efficiency when thenewer manufacturing generation is being adopted. Lithography processrequires maintaining throughput efficiency while assuring product yieldbetter than previous generations. This demands wider lithography processwindow and fewer process defects while contending with bigger FPDsubstrates. As discussed above, there are numerous shortcomings with theexisting exposure tool configurations. One of the major shortcomings isassociated with the use of a mask. The size of the mask is too large tobe manufactured cost effectively. This shortcoming continues to grow asthe size of the mask must increase in order to keep up with futuregenerations of FPDs. Therefore, there is a need for an improved imagingwriter system that addresses the issues of the conventional tools andapproaches.

SUMMARY

The present invention relates to systems and methods for applying maskdata patterns to substrate in a lithography manufacturing process. Inone embodiment, the imaging system includes a plurality of spatial lightmodulator (SLM) imaging units, where each of the plurality of SLMimaging units includes one or more illumination sources, one or morealignment sources, one or more projection lenses, and a plurality ofmicro mirrors configured to project light from the one or moreillumination sources to the corresponding one or more projection lens.The imaging system further includes a controller configured to controlthe plurality of SLM imaging units, where the controller tunes each ofthe SLM imaging unit individually in writing a mask data to a substratein a lithography manufacturing process.

In another embodiment, a parallel imaging writer system includes aplurality of spatial light modulator (SLM) imaging units, where each ofthe plurality of SLM imaging units includes one or more illuminationsources, one or more alignment sources, one or more projection lenses,and a plurality of micro mirrors configured to project light from theone or more illumination sources to the corresponding one or moreprojection lens. The parallel image writer system further includes acontroller configured to control the plurality of SLM imaging units,where the controller further includes logic for receiving a mask datapattern to be written to a substrate, logic for processing the mask datapattern to form a plurality of partitioned mask data patternscorresponding to different areas of the substrate, logic for assigningone or more SLM imaging units to handle each of the partitioned maskdata pattern, and logic for controlling the plurality of SLM imagingunits to write the plurality of partitioned mask data patterns to thesubstrate in parallel.

In yet another embodiment, a method for applying mask data patterns tosubstrate in a lithography manufacturing process includes providing aparallel imaging writer system, where the parallel imaging writer systemincludes a plurality of SLM imaging units arranged in one or moreparallel arrays, receiving a mask data pattern to be written to asubstrate, processing the mask data pattern to form a plurality ofpartitioned mask data patterns corresponding to different areas of thesubstrate, assigning one or more SLM imaging units to handle each of thepartitioned mask data pattern, and controlling the plurality of SLMimaging units to write the plurality of partitioned mask data patternsto the substrate in parallel.

In yet another embodiment, a method for applying mask data patterns tosubstrate in a lithography manufacturing process includes providing aparallel imaging writer system which has a plurality of spatial lightmodulator (SLM) imaging units arranged in one or more parallel arrays;receiving a mask data pattern to be written to a substrate, processingthe mask data pattern to form a plurality of partitioned mask datapatterns corresponding to different areas of the substrate, assigningone or more SLM imaging units to handle each of the partitioned maskdata pattern, controlling the plurality of SLM imaging units to writethe plurality of partitioned mask data patterns to the substrate inparallel, controlling movement of the plurality of SLM imaging units tocover the different areas of the substrate, and controlling movement ofthe substrate to be in synchronization with continuous writing of theplurality of partitioned mask data patterns.

In yet another embodiment, a parallel imaging writer system includes aplurality of spatial light modulator (SLM) imaging units, where each ofthe plurality of SLM imaging units includes one or more illuminationsources, one or more alignment sources, one or more projection lenses,and a plurality of micro mirrors configured to project light from theone or more illumination sources to the corresponding one or moreprojection lens. The parallel imaging writer system further includes acontroller configured to control the plurality of SLM imaging units, andthe controller synchronizes movements of the plurality of SLM imagingunits with movement of a substrate in writing a mask data to thesubstrate in a lithography manufacturing process.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned features and advantages of the invention, as well asadditional features and advantages thereof, will be more clearlyunderstandable after reading detailed descriptions of embodiments of theinvention in conjunction with the following drawings.

FIG. 1 illustrates a conventional configuration of projection exposuretool used for scanning mask patterns onto FPD substrate.

FIG. 2 illustrates a conventional mask making exposure toolconfiguration.

FIG. 3 illustrates an exemplary digital micro-minor device according toembodiments of the present invention.

FIG. 4 illustrates a DMD-based projection system according toembodiments of the present invention.

FIG. 5 illustrates an exemplary specular state and diffraction state ofa grating light valve (GLV) device according to embodiments of thepresent invention.

FIG. 6 illustrates an example of a compact SLM imaging unit according toembodiments of the present invention.

FIG. 7 illustrates an exemplary parallel array of SLM imaging unitsaccording to embodiments of the present invention.

FIG. 8 illustrates the corresponding top-down view of the parallel arrayof SLM imaging units of FIG. 7 according to embodiments of the presentinvention.

FIG. 9 illustrates a comparison of a conventional single lens projectionsystem versus the localized process window optimization using thearrayed imaging system according to embodiments of the presentinvention.

FIG. 10 illustrates a method for optimizing localized unevenness insubstrate according to embodiments of the present invention.

FIG. 11 illustrates an application of a mask data structure according toembodiments of the present invention.

FIG. 12 illustrates a method of parallel array voting exposuresaccording to embodiments of the present invention.

FIG. 13 illustrates a method for implementing redundancy in the imagingwriter system according to embodiments of the present invention.

FIG. 14 illustrates the Keystone border blending method according toembodiments of the present invention.

FIG. 15 illustrates a method for placing SLM imaging units in an arrayaccording to embodiment of the present invention.

FIG. 16 illustrates an exemplary implementation of a maskless imagingwriter system for making flexible display according to embodiments ofthe present invention.

FIG. 17 illustrates a SLM imaging unit according to embodiments of thepresent invention.

FIG. 18 illustrates a method of using a linear array of SLM imagingunits for roll-to-roll maskless lithography according to embodiments ofthe present invention.

FIG. 19 illustrates a method of using a two dimensional array of SLMimaging units for roll-to-roll maskless lithography according toembodiments of the present invention.

FIG. 20 illustrates a method of imaging plurality of substrate sizesusing maskless lithography according to embodiments of the presentinvention.

FIG. 21 illustrates a method for positioning each SLM imaging unitcorresponding to conditions of localized substrate surface according toembodiments of the present invention.

FIG. 22 illustrates a method for detecting focus of pixels according toembodiment of the present invention.

FIGS. 23 a-23 c illustrate exemplary apparatuses for detecting focus ofa SLM imaging unit on-the-fly according to embodiments of the presentinvention.

FIG. 24 illustrates an exemplary imaging pattern where pixel votingexposure may be applied according to embodiments of the presentinvention.

FIG. 25 illustrates a method for improving DOF through pixel votingexposures according to embodiments of the present invention.

Like numbers are used throughout the specification.

DESCRIPTION OF EMBODIMENTS

System and method are provided for applying mask data patterns tosubstrate in a lithography manufacturing process. The followingdescriptions are presented to enable any person skilled in the art tomake and use the invention. Descriptions of specific embodiments andapplications are provided only as examples. Various modifications andcombinations of the examples described herein will be readily apparentto those skilled in the art, and the general principles defined hereinmay be applied to other examples and applications without departing fromthe spirit and scope of the invention. Thus, the present invention isnot intended to be limited to the examples described and shown, but isto be accorded the widest scope consistent with the principles andfeatures disclosed herein.

Some portions of the detailed description that follows are presented interms of flowcharts, logic blocks, and other symbolic representations ofoperations on information that can be performed on a computer system. Aprocedure, computer-executed step, logic block, process, etc., is hereconceived to be a self-consistent sequence of one or more steps orinstructions leading to a desired result. The steps are those utilizingphysical manipulations of physical quantities. These quantities can takethe form of electrical, magnetic, or radio signals capable of beingstored, transferred, combined, compared, and otherwise manipulated in acomputer system. These signals may be referred to at times as bits,values, elements, symbols, characters, terms, numbers, or the like. Eachstep may be performed by hardware, software, firmware, or combinationsthereof.

Embodiments of the present invention use spatial light modulator (SLM)based image project devices. Two types of SLM based image projection maybe used, one is the digital micro-minor device (DMD) and the other isthe grating light valve (GLV). Both types of devices may be produced byusing micro-electro-mechanical (MEM) manufacturing methods.

FIG. 3 illustrates an exemplary digital micro-minor device according toembodiments of the present invention. In this example, a single DMD dieis represented by numeral 302 and an enlarged and simplified view of thesame DMD die is represented by numeral 304. DMD can be addressed bytilting micro-mirrors in fixed angles, typically around ±10° or ±12°, toact as spatial light modulator (SLM). The minor surface of DMD is highlyreflective to the incident illumination. Each micro-mirror can bemanipulated to tilt (represented by numeral 306) or left un-changed(represented by numeral 308) by the transistor controller underneath. Inone implementation, DMD may have pitch dimension of about 14 μm withabout 1 μm space between each micro-mirror. The pixel count on a singleDMD die may be 1920×1080 mirror pixels, compatible to high definitiontelevision (HDTV) display specifications.

FIG. 4 illustrates a DMD-based projection system according toembodiments of the present invention. In this example, the micro-minorhas three states: 1) “On” State 402 at about +10° tilting angle, 2)“Flat” State 404 at no tilt, and 3) “Off” State 406 at about −10°tilting angle. When a ray of light beams shine from a light source 408located at −20° angle to the DMD, they can reflect light beams directlyto pass through projection lens 410 to form bright spots on the displaysubstrate, for the minors that are at “On” State or “1” in binary. Formirrors that are at “Flat” State and “Off” State, or the “0”, the lightbeams reflected in an angle falling outside of the collection cone ofthe projection lens, at approximately −20° and −40° respectively. Henceno light pass though from those mirror sites, dark spots are then formedon the display substrate. Since each of micro-minor reflection cannot bevisually resolvable by human eyes, a gray shade can be constructed bycombining a group of light and dark spot pixels in a ratio whenprojected. This method enables the projection of realistic images withmillion shades of grays and colors.

Note that the higher diffraction orders of diffraction beam from the“Flat” State and the 2^(nd) order of diffraction beam from the “Off”State can still fall within the collection cone angle of the projectionlens. This may create unwanted flare that reduces the desire imagecontrast. According to embodiments of the present invention, a preciselyaimed and focused high intensity illumination source may be used toincrease the pixel diffraction efficiency to optimize the design of theprojection optics using DMD for imaging writer.

According to other embodiments of the present invention, GLV is anotherapproach for implementing image projection. The top layer of GLV deviceis a linear array of materials, also referred to as ribbons, which arehighly reflective. In one embodiment, ribbons may be 100-1000 μm long,1-10 μm wide and closely spaced by 0.5 μm. The imaging mechanism of GLVis essentially addressable dynamic diffraction grating. It functions asa phase modulator. A GLV device may include a group of six alternativeribbons deflected to form dynamic diffraction grating.

FIG. 5 illustrates an exemplary specular state and diffraction state ofa GLV device according to embodiments of the present invention. When theGLV ribbons (in cross-sectional view) are co-planar (represented bynumeral 502), the incident light is reflected specularly, i.e. all inthe 0^(th) diffraction order. When incident light shines on a group ofribbons, where ribbons are deflected in an alternating fashion(represented by numeral 504), and a diffraction pattern is formed withstrong ±1^(st) orders but with suppressed 0^(th) order. A high contrastreflection image can be constructed by filtering out either 0^(th) or±1^(st) orders. That is, no image may be formed if to re-capture all of0^(th) or ±1^(st) orders in the objective lens. Unlike DMD, the entireimage in a field of view as formed by GLV is based on scanning line byline since there may be one line of diffraction images are formed by thelinear array of grating ribbons at one time.

As discussed in association with FIG. 1 and FIG. 2, in order to achievethe throughput requirements, high powered illumination sources for theconventional systems are necessary. In one example, high pressure Hgshort-arc lamp in the kilo-Watts range is used. Another example is touse high powered Excimer laser. Due to the use of high powerillumination sources, the illumination light path needs to be directedfrom a distance to reduce the heat generated and then be folded for aright illumination. This type of configuration separates theillumination and SLM imaging system into two separate units and thelight path and the lens are perpendicular to each other.

To address the limitation of the conventional systems and approaches,the improved exposure tool configuration reduces the need to usehigh-powered illumination sources. An in-line imaging system isconfigured where each of the imaging unit includes the SLM, theillumination sources, the alignment illumination, the electroniccontrol, and the imaging lens. This system may have a lower exposurethroughput when using low powered LED and diode laser illuminationsources. However, the exposure throughput may be increased by using alarger number of imaging units. One of the benefits of using a compactSLM imaging unit is that a scalable array of such units may be packedfor different imaging applications. In one application example, whenarrayed with more than 1000 such compact SLM imaging units, the writingthroughput exceeds the existing multi-wavelength, mask-based exposuretool configuration.

FIG. 6 illustrates an example of a compact SLM imaging unit according toembodiments of the present invention. In this example, the compact SLMimaging unit includes a spatial light modulator 602, a set ofmicro-mirrors 604, one or more illumination sources 606, one or morealignment light sources 608, and a projection lens 610. The illuminationsource 606 may be implemented with LED or diode laser having wavelengthless than 450 nm with blue light or near UV. The alignment light source608 may be implemented with a non-actinic laser source or LED forthrough-the-lens focus and alignment adjustment. The projection lens 610may be implemented with a lens having a 5× or 10× reductions. As shownin FIG. 6, the illumination sources 606 and the alignment light source608 are all placed outside of the collection cone angle of theprojection lens. In this exemplary implementation, off-the-shelfprojection lenses with numerical aperture NA of 0.25 at resolving powerof about 1 μm may be used. The relatively low NA ensures better depth offocus (DOF). In one lithography process example, using NA of 0.25 for 1μm photo resist CD target, the DOF may be >5.0 μm. The resolution andDOF calculations are based on Rayleigh criterion:

Minimum feature resolution=k ₁(λ/NA)

DOF=k ₂(λ/NA ²)

where, k₁ and k₂ are process capability factors. According to animplementation of lithography manufacturing process based on Novolakchemistry photoresist, k₁ is in the range from 0.5 to 0.7, k₂ is from0.7 to 0.9, and λ refers to the exposure wavelength.

In order to fit a compact form factor, illumination sources may be blue,near UV LED, or semiconductor diode laser. To get sufficient intensity,in one design example, the illumination sources are placed close to theSLM surface and there may be multiple illumination sources placedsurrounding the SLM. The SLM may be DMD or GLV with proper optical lensdesign matched to each. In one example, the targeted intensity level atthe substrate may be between 10-100 mW per square centimeter of theactinic exposure wavelength.

In this exposure tool configuration example, the housing for theelectronic control boards for each compact imaging system conforms to aspecified compact factor. It is located on the top of the SLM, away fromthe illumination sources. This facilitates ventilation and heatdissipation. The physical dimension for a single compact SLM imagingunit depends on the required imaging performance and the availablecomponents use off-the-shelf supply, such as the projection lens, LED ordiode laser illumination sources, and focus/alignment diode laser, eachwith required room for heat dissipation. Another approach is to havecustom design for the components so that the physical dimension for asingle SLM imaging unit can be trimmed to an even more compact form. Acustom designed SLM imaging unit may have a dimension of approximately 5cm×5 cm in 2D cross-section compared to a dimension of approximately 10cm×10 cm using off-the-shelf supply.

For the G10 FPD manufacturing, a typical substrate size is 2880 mm×3130mm. Using the physical dimension of compact SLM imaging lens, a systemmay include hundreds of compact SLM imaging units arranged into an arrayof parallel imaging units. FIG. 7 illustrates an exemplary parallelarray of SLM imaging units according to embodiments of the presentinvention. In this example, the image writing can be performed by 600 to2400 parallel arrays of SLM imaging units (702, 704, 706, 708, etc.)simultaneously and each parallel array may includes multiple SLM imagingunits.

According to embodiments of the present invention, the exposurethroughput may be determined using a known example throughput of a SLMmask writer, such as 20 hours for the mask size of 1300 mm×1500 mm, maybe used as a starting point. Throughput depends on the intensity levelat the substrate plane. In this approach, for the intensity level of 50mW per square centimeter, achievable with LED or diode laser sources,and for the nominal exposure energy of 30 mJ/sq-cm-sec, the exposuretime is approximately 0.6 seconds. In another approach, where theexposure tool uses high-powered illumination source, the intensity levelat the substrate is at least 200 mW per square centimeter or higher. Thethroughput for such a mask-based stepper/scanner system is about 50 G8FPD substrate plates per hour. By taking into account of bothhigh-powered and low-powered illumination sources, the throughputestimation in one example is from 25 to 100 substrates per hour,depending on the density of parallel SLM imaging units used in thearray. This shows that such an array parallel exposure configuration iscompetitive economically.

FIG. 8 illustrates the corresponding top-down view of the parallel arrayof SLM imaging units of FIG. 7 according to embodiments of the presentinvention. In this example, each row or column may represent a parallelarray of SLM imaging units, and each parallel array may include multipleSLM imaging units 802. Lithography manufacturing yield is directlyrelated to process window. Here process window refers to the range focussettings in conjunction with the range of exposure dose settings thatcan print feature CDs within the specifications. That is, for a morerobust process window, it can tolerate wider defocus settings and/orexposure dose settings. A wider process window may produce a betterproduct yield. With bigger substrate for each newer generation,lithography window becomes smaller. This is mainly due to the moretendencies for larger and thinner substrate material to warp or sag. Toaddress this issue, the solution calls for tightening thickness andsurface uniformity specifications for substrate material. For mask-basedexposure tool, maintaining uniformity and focus control over an exposurefield that is larger than about two meters in one side is not only veryexpensive but also technologically challenging. To assure a workableprocess window, exposure tool need to be able to optimize focus andillumination in both local and global fashions.

As shown in FIG. 8, this array parallel exposure system addresses theissues discussed above. This is because each of the compact SLM imagingunits can be optimized locally for better illumination and focuscorresponding to its own exposure area. That ensures a better processwindow in each exposure area of the SLM imaging unit. The entire processwindow is then improved globally using optimized contributions from theSLM imaging units.

FIG. 9 illustrates a comparison of a conventional single lens projectionsystem versus the localized process window optimization using thearrayed imaging system according to embodiments of the presentinvention. On the left hand side of FIG. 9, the conventional single lensprojection system 902 must be tuned to a compromised focal plane 904, asshown in dotted line. The solid line 906 represents the actual surfacecontour of the substrate in cross-sectional view. The double arrow 908indicates the best focus setting corresponding to a single lens that isused to image the pattern. The lines with round heads 910 represent themaximum contour range correspond to each imaging lens and the dot-dashedlines indicate the upper and lower limits of the focus range.

As shown in FIG. 9, for the conventional single lens projection system,the large-sized substrate curvature may have already exceeded the focusrange of the lens. The center of focus may be only marginally acceptablewith respect to both of the peak and valley curvatures in the substrate.The overall process window becomes limited. On the other hand, the righthand side of FIG. 9 shows an improved projection system with imagingunits arranged in an array. The focus 914 of an imaging unit 912 can betuned individually for each localized area covered. As a result, eachfocus setting can be placed well within the focus control limits asrepresented by the lines 916. In addition to the ability to fine tunefocus in each of the local area covered, the illumination of eachimaging unit may also be adjusted to achieve a better uniformitycompared to the adjustment may be performed by a single lens system.Therefore, a more robust process window is achieved by using the arrayedimaging unit system.

FIG. 10 illustrates a method for optimizing localized unevenness insubstrate according to embodiments of the present invention. In thisexample, region of uneven contours are detected in the substrate asindicated by numeral 1002. One method of tuning optimization is to applya focus averaging scheme for the uneven local exposure areas that areassociated with a SLM imaging unit as well as the surrounding areasassociated with SLM imaging units in the neighborhood of the SLM imagingunit of interest. The more imaging units in the neighborhood of theuneven areas that can be included for averaging, the better globalizedoptimization can be achieved. A person skilled in the art wouldappreciate that other averaging techniques may be applied to thedisclosed imaging system for the entire substrate plate to achieve amore uniform image globally across the whole substrate.

In one implementation, the mask data format for thin film transistor(TFT) based LCD display may be implemented as follows. Note that thehierarchical stream data format GDSII may be used for taping out maskdata, but this type of mask data format may not be well-suited for thisparallel SLM imaging system. To convert from hierarchal mask data toflat format, this can be done by using an off-the-shelf CAD softwareprogram. However, after flattened the mask data, further processing themask data is needed. Mask data structure is used in conjunction with thearrayed parallel imaging writer system to produce higher quality images.

For the arrayed parallel imaging writer system, the mask data structuremay be flattened and may be partitioned into pieces of a predefined sizeto properly or evenly feed to every SLM imaging unit. The mask datastructure includes information that indicates the placement for eachpiece of mask data relative to its respective imaging unit. Moreover,the mask data structure includes information that specifies how featuresthat span multiple imaging units will be divided among them. The dataplacement tuning can be recognized via the mask data structure that isrelated to the adjacent mask data areas from the adjacent imaging units.

FIG. 11 illustrates an application of a mask data structure according toembodiments of the present invention. In this example, a hierarchicaldescription of a mask data in terms of multiple levels of mask datainstances 1102 is first flattened to form a flattened mask data 1104.Then, the flattened mask data 1104 is partitioned into multiplepartitioned mask data patterns. One such partitioned mask data patternis shown as a shaded area 1106, which is also shown as the center blockin the nine blocks (separated by dotted lines) at the bottom of FIG. 11.Sufficient mask patterning overlaps between the adjacent imaging units,shown as horizontal and vertical strips 1108, are needed to ensureuniform pattern blending around the borders, where each block representsa partitioned mask data to be imaged by one or more SLM imaging units.According to embodiments of the present invention, the partitioned maskdata includes a first set of identifiers for identifying run-inconditions of mirror pixels within a SLM imaging unit and a second setof identifiers for identifying run-out conditions of mirror pixelswithin a SLM imaging unit. A run-in condition occurs where excessivepixels are found in an area between two SLM imaging units. A run-outcondition occurs where insufficient pixels are found in an area betweentwo SLM imaging units. Each partitioned mask data pattern is fed to itscorresponding SLM imaging unit for processing, where each SLM imagingunit writes its associated partitioned mask data pattern inpredetermined overlapped areas using adjacent SLM imaging units asreferences to ensure the imaging blending and uniformity meet designcriteria. The partitioned mask data pattern may be optimized to enableparallel voting exposures for feature CD uniformity. In this case, aparallel voting exposure scheme is used in minimizing processingvariables that may negatively impact CD uniformity. The elimination ofGaussian speckles due to the use of diode laser is accomplished by usingsufficient number of micro-mirror pixel exposures for voting.

FIG. 12 illustrates a method of parallel array voting exposuresaccording to embodiments of the present invention. The method firstsends the mask data to each of SLM imaging unit in a row-by-row fashion,then to flash the row of micro-minor pixels starting from one end of therow to the next until reaching the opposite end. In one example, themethod starts with block 1201 and flashes the bottom row of micro-mirrorpixels. It then moves block 1202 and flashes the second row from thebottom row of micro-minor pixels. In block 1203, the third row from thebottom row of micro-minor pixels is flashed. The method continuesthrough blocks 1204, 1205, 1206, 1207 and flashes the corresponding rowof micro-mirror pixels. And in block 1208, the method has traversed thelast row of micro-mirror pixels (which is the top row) in thisparticular example. The same walking-row of micro-minor pixels loopsagain and again from the start to the end. The looping of thewalking-row corresponds to exposure actions for writing patterns onsubstrate. Because micro-mirror flashing rate is fast enough, thefeature patterns are exposed by the fast moving walking-row numeroustimes until nominal exposures level is accumulated. Thus, such a patternwriting scheme is, in effect, done by voted exposures from numerousmicro-mirror pixels. By moving substrate stage in a coordinated pace andorientation, the writing for entire substrate is carried out with thesame voting exposure scheme.

The walking-row approach illustrated in FIG. 12 is one example oflooping walking-row for making one style of parallel voting exposurelocally or sub-locally for every imaging unit. In other embodiments,looping methods based on column or diagonal row/column may be used foreffective parallel voting exposures. Additional voting schemes can bederived such as interlaced walking-rows from the two adjacent SLMimaging units or to use multiple walking orientations with several datarows, etc., may be employed to improve printing performance, althoughpossibly at the expense of additional stage motion.

For array parallel exposure under heavy production environment,redundancy or fault-tolerance may be built-in to prevent production flowfrom interruption. That is, as the exposure control routine detects afailure of an SLM imaging unit, it then takes action to disable theproblematic imaging unit, redistributes the mask data to one or more ofthe adjacent imaging units, and then has these adjacent imaging unitscomplete the exposure tasks before unloading the exposed plate. Thiscorrective exposure routine continues until the full batch-load ofplates is done. The process continues until both the imaging performanceand throughput hit are considered acceptable.

FIG. 13 illustrates a method for implementing redundancy in the imagingwriter system according to embodiments of the present invention. In thisexample, after detecting that image unit 212 has malfunctioned, thisunit is shut down. One of the 8 adjacent imaging units may be selectedto take over. In this case, the writing for the unit 212 area is doneafter exposures of other areas have been accomplished.

Micro mismatched (local to local) borders from the two adjacent SLMimaging units can occur when imaging distortions result from substratewarping or sagging. This is represented by numeral 1402, where datapatterns fall outside of the boxed area. In this case, the patternblending in the overlapped areas needs to be optimized. FIG. 14illustrates the Keystone border blending method according to embodimentsof the present invention. As shown in FIG. 14, the method turns onmicro-mirror pixels at the selected border end 1404 that allows betteroverlap matching to the adjacent imaging unit writing area 1406. Personsskilled in the art would appreciate that other approaches may be used toachieve border blending by turning on micro-mirror pixels selectively atdesired sites.

According to some embodiments, blending may be performed by turning onselected micro-mirror pixels in alternate or complementary mannerbetween the adjacent overlapping borders. According to yet some otherembodiments of the present invention, mixing walking-row exposure votingaction together with additional pixel turning at selected sites may beused to achieve better blending.

In order to achieve the intended alignment accuracy and precision forthe array parallel imaging system, the method decomposes the alignmentscheme into several accuracy precision levels in cascade. Firstalignment level is to aim for global alignment accuracy level, next isto narrow into intermediate level of accuracy precision. Using thisbottom-up approach, the method achieves the desired accuracy precisionlevel.

In one approach, three accuracy precision levels are defined: the unitlens array placement, the lens center tuning, and the micro-minorimaging data manipulation. FIG. 15 illustrates a method for placing SLMimaging units in an array according to embodiment of the presentinvention. This method provides global placement accuracy of the SLMimaging units 1502 in the millimeters range. Next, for each SLM imagingunit, the position of projection lens assembly is electronically tunedto precision in micrometer range. This is done by aligning the lenscenter using HeNe laser (or other non-actinic alignment light source) toa known reference position on the stage. Finally the micro-mirrors arecontrolled to achieve alignment requirements in precision of nanometerrange.

According to embodiments of the present invention, the alignment processfor making exposure may be carried out as follows:

1) Using a known reference site on the stage, the lens center for eachSLM imaging unit in the array is first calibrated. This allowsconstructing a mathematical grid array points in reference to thephysical lens array.

2) For the first masking layer, when there is no alignment marksprinted, the plate alignment is done mechanically relying mainly on thestage precision.

3) When the substrate plate has alignment marks throughout the plate asprinted from the previous masking layer, these alignment marks can bedetected by the corresponding SLM imaging units. From this, a grid mapis constructed in reference to the actual image locations that are onthe substrate plate.

4) By comparing the two grid maps (SLM imaging unit vs. printedalignment marks detected from the substrate), build a grid map matchingmathematical model for stage travel guide.

5) In one example, by considering 2400 array SLM imaging units for G10substrate, the maximum stage travel distance is about 120 mm in eitherhorizontal (X) or vertical (Y) direction. This is included for grid mapmatching calculation. Note that such a stage travel distance is rathersmall hence technologically advantageous compared to making the stagetravels in full plate width and length required by using mask-basedexposure tool for the G10. The G10 plate substrate can have a heavymass. The shorter stage distance traveled while carrying such a heavymass, the better system accuracy performance may be achieved.

6) To fine-tune sub-micron alignment accuracy, the method embeds thecorrection factors into the mask data that is being sent to thecorresponding imaging unit. That is, the correction factors for everyimaging unit may be different depending on the relative imaginglocations on the substrate. They can also be different from plate toplate since the substrate warping condition may be different and may bedetected ahead of the time before exposing each plate.

FIG. 16 illustrates an exemplary implementation of a maskless imagingwriter system for making flexible display according to embodiments ofthe present invention. As shown in FIG. 16 the maskless image writersystem 1600 is formed by one or more arrays of SLM imaging units, where1602 is an example of one of the SLM imaging units. The one or morearrays of SLM imaging units may be formed into a particular shape, forexample circular, which may be required by a specific application. Inanother exemplary implementation, the maskless imaging writer system maybe configured to make non-flexible displays.

FIG. 17 illustrates a SLM imaging unit according to embodiments of thepresent invention. The SLM imaging unit includes blue and red diodelasers 1702, an aperture 1704, a lens 1706, a spherical mirror 1708, aDMD 1710 mounted on a printed circuit board 1712, a beam dump 1714, abeam splitter 1716, a CCD camera 1718, and a lens assembly 1720. Theblue and red diode lasers 1702 further includes a red laser diode(non-actinic) 1722 and four blue laser diodes (actinic) 1723, 1724, 1725and 1726. The laser diodes may be arranged in the example as shown inFIG. 17. The center red laser diode is non-actinic and it is mainly usedfor alignment or catching for initial focus setting. The four blue laserdiodes are actinic and they are used for making exposure. Depending onthe physical size of the laser diode package, other types of arrangementusing different numbers of laser diodes are possible as long as auniform intensity can be achieved. In another approach, the actinicillumination can also be delivered via optical fiber bundles. In that,each laser diode shines on the one end of the optical fiber bundle andlet fiber carry the actinic light to shine from the other end of theoptical fiber bundle. In other embodiments, LEDs may be used instead ofdiode lasers. In this arrange example, the blue LEDs can be placedtightly together in such a way to achieve uniform intensity whilemultiple red LEDs can be placed in relative locations that may beconfigured to achieve alignment and initial focusing purposes. In thisexample, the blue and red diode lasers 1702 project light to thespherical mirror 1708 through the aperture 1704 and the lens 1706. Thelight is then reflected from the spherical minor 1708 to the DMD 1710.According to the state of each minor in the DMD, the light may be sentto the beam dump 1714, or to a substrate through the lens assembly 1720.The image thus created on the substrate reflects back upward throughlens 1720 and beam splitter 1716 to CCD camera 1718.

FIG. 18 illustrates a method of using a linear array of SLM imagingunits for roll-to-roll maskless lithography according to embodiments ofthe present invention. In this example, the SLM imaging units 1802 arearranged as a single line array as shown in FIG. 18. The substrate 1804may be controlled to move along the direction of substrate movement (theX direction) and the linear array of SLM imaging units 1802 may becontrolled to move back and forth perpendicular to the direction ofsubstrate movement (the Y direction) in the plane of the substrate 1804.The exposure of the linear array of SLM imaging units can be tuned toprocess certain area of the substrate 1804 in synchronization with theroll-to-roll substrate movement. In this way, the linear array of SLMimaging units may be controlled to image a substrate that has physicaldimensions larger than the size of the linear array of SLM imagingunits. Because of the ability to control the SLM imaging units to movein the direction of substrate movement as well as in the directionperpendicular to the substrate movement, the image writer system shownin FIG. 18 overcomes the size limitations of the physical masks requiredin the conventional methods described in the '779 patent and the Ahnarticle.

FIG. 19 illustrates a method of using a two dimensional array of SLMimaging units for roll-to-roll maskless lithography according toembodiments of the present invention. This figure shows a top view of atwo dimensional SLM imaging array 1902, where each circle represents aSLM imaging unit. Similar to the example shown in FIG. 18, the substrate1904 may be controlled to move in the X direction and the twodimensional array of SLM imaging units 1902 may be controlled to moveback and forth in the Y direction in the plane of the substrate 1904.The exposure of the two dimensional array of SLM imaging units can betuned to process certain area of the substrate 1904 in synchronizationwith the roll-to-roll substrate movement. In this way, the twodimensional array of SLM imaging units may be controlled to image asubstrate that has physical dimensions larger than the size of the twodimensional array of SLM imaging units. Thus, the image writer systemshown in FIG. 19 overcomes the size limitations of the physical masksrequired in the conventional methods described in the '779 patent andthe Ahn article. Note that in some embodiments, the two dimensionalarray of SLM imaging units may be formed in a staggered or non-staggeredarray formation.

FIG. 20 illustrates a method of imaging plurality of substrate sizesusing maskless lithography according to embodiments of the presentinvention. Similar to the method described in FIG. 19, the image writersystem also employs a two dimension array of SLM imaging units 2002.Since the two dimensional array of SLM imaging units 2002 may becontrolled to receive and process imaging data automatically in acontinuous fashion, the image writer system can transition from onesubstrate design to a different substrate design by loading a new TFTmask database seamlessly without the need to stop and change to a newmask as required by the conventional methods described in the '779patent and the Ahn article. In the example shown in FIG. 20, differentsized substrate designs, such as 2006, 2008, 2010, 2012, and 2014 can beprocessed on-the-fly as the roll-to-roll substrate containing thedifferent sized substrate designs move by the two dimensional array ofSLM imaging units 2002.

FIG. 21 illustrates a method for positioning each SLM imaging unitcorresponding to conditions of localized substrate surface according toembodiments of the present invention. In this example, the methodexamines the unevenness of the substrate surface 2104 during exposure,and adjusts the linear array of SLM imaging units 2102 accordingly. Inthis example, the uneven substrate 2104 is excessively shown toillustrate the benefit of having optimum height adjustment for each SLMimaging unit. This allows achieving auto-focus tuning to come within therange of DOF for intended resolution CD from 1 to 5 μm. This method isfurther described in the following sections.

In one approach, for printing TFT based photo voltaic (PV) panel, theminimum features CD can be more than 50 μm. In this printing resolutionrange, it often thought that ink-jet printing could be a less costlyoption. However, one major drawback for ink-jet printing is defect-pronedue to ink mist, a side effect that comes with ink jet droplet stream.Ink-jet printing is inherently not as clean as lithography process. Itmay be suited for patterning mask features that do not form activedevice or mainly for passive viewing purpose. For production worthy ofmaking active TFT device with roll-to-roll printing, scalable array ofSLM imaging units provides a better solution for maskless lithographybecause it produces better device yield. In this method, a magnificationprojection is used for maskless imaging. That is, instead of using areduction objective lens, the exposure lens of the SLM imaging unitemploys an enlargement objective lens that can magnify product featuresize from 25 μm to a couple of hundred μm in a controlled fashion.

In order to maintain best focus over a substrate that may not beperfectly flat, one way is to monitor and adjust the focus of the SLMimaging unit during exposure. FIG. 22 illustrates a method for detectingfocus of pixels according to embodiments of the present invention. Oneapproach for monitoring focus is to use a through-the-lens monitoringcamera to capturing images of the exposure in progress. After images arecaptured, an analysis of dark-light pixel image captured, in comparisonwith what would be expected for the exposure pattern, can readily derivea relative measure of the amount of defocus. As shown in the example ofFIG. 22 is a pair of light and dark pixels (2202 and 2204) with in-focus(2206 and 2208) and an out-of-focus 2210 conditions. At the boundarytransition from dark to light area, the in-focus pair exhibits a sharpertransition pattern, whereas the out-of-focus pair has a blurredtransition. The degree of blurred transition can be mapped to refer tothe amount of defocus. In other approaches, one may monitor and analyzespatial frequencies in the image. Since focus errors preferentiallyreduce the higher spatial frequencies, one may assess the amount ofdefocus by comparing the loss of high frequency components of the imagecaptured. Yet another method is to monitor and analyze the imagecontrast from a group of light-dark patterns, with image contrast beingthe best at optimum focus setting. And the degrees of contrast lost canbe referred to the amount of de-focus.

Although the methods described above are effective focus monitors of thesize of focus error, they do not directly provide any indication of thedirection of the error. To address this issue, the system may, undersoftware control, constantly vary the focus slightly over a rangecentered on the target focus, and update the target focus position tokeep it at the best focus. This can most sensitively be determined bybalancing the errors at the two extremes of the range. It may beadvantageous, however, to avoid the need to intentionally defocus theexposure image. One way to achieve this is to perturb the focus of thecamera in a controlled fashion, without altering the focus of theexposure image. This can be done on a through-the-lens monitor camera byaltering the effective optical path length between the camera and theobjective lens. To a first order approximation, changing the focallength on the camera side of the lens (f₂ in the diagram) has the sameeffect as changing f₁ by the same percentage. This focus change can beeffected by vibrating the camera in and out, reflecting the image off amirror that vibrates, or as shown in FIG. 23 a, by passing the lightthrough a spinning disk with segments having different thicknessesand/or refractive indices, to give the desired variation in effectiveoptical path length. This is as shown as the first OPD 2316 and thesecond OPD 2326. Similarly, the image could be reflected off a mirroreddisk, with segments at different heights.

FIG. 23 a illustrates an exemplary apparatus for detecting focus of aSLM imaging unit on-the-fly according to embodiments of the presentinvention. As shown in FIG. 23 a, the apparatus includes an imagingsource 2302, a beam splitter 2304, an objective lens 2306 and itshousing 2308. An example of the imaging source 2302 is shown in FIG. 17,including the components 1702 to 1714. The apparatus also includes afirst camera sensor 2310 (also referred to as the camera or sensor forshort), a first motor 2312, a first refractive disk 2314, and a firstoptical path difference (OPD) modifier 2316. The first OPD modifier 2316may be formed from a circular optical device 2317, where the circularoptical device 2317 may be made with multiple sectors (for example 2318)and each sector is made with different refraction index material, ormade with the same refractive index material but with differentthickness than can cause optical path difference.

Another way of determining the focus adjustment direction is to have twocameras that can capture the images from different optical path lengthsas shown in FIGS. 23 b and 23 c. FIGS. 23 b-23 c illustrates two otherexemplary apparatuses for detecting focus of a SLM imaging uniton-the-fly according to embodiments of the present invention. Inaddition to the elements shown in FIG. 23 a, these exemplary apparatusfurther includes a second camera sensor 2322 (also referred to as thecamera or sensor for short), and a second optical path difference (OPD)modifier 2326. FIG. 23 c also includes a third OPD modifier 2330. Thesecond and third OPD modifiers 2326 and 2330 may be formed in a similarfashion as the first OPD modifier 2316. When with two camera sensors2310 and 2322 are used, the two respective OPDs 2316 and 2326 withdifferent refractive indexes can be set up to determine focus adjustmentdirection. In another embodiment, the different OPDs 2316 and 2326 areeffected simply by placing the respective cameras 2310 and 2322 atdifferent physical distances,

The examples shown in FIGS. 23 b-23 c examine the images from firstcamera sensor to second camera sensor to compare and analyze the focusadjustment direction, and adjust focus setting to equalize the defocusobserved in the two camera sensors, thus assuring that the best focus isachieved at an OPD midway between the two camera sensors. Here, thefirst and second camera sensors are configured to observe the substratewith complementary focus offsets to determine direction of a targetfocus. Yet another method is to avoid adjusting focus by moving theobjective lens up and down, this is to place the third OPD 2330 abovethe housing 2308 of the objective lens 2306 to effect the focusadjustment by changing the effective optical path length.

The on-the-fly focus monitor and adjustment may be performed as follows:

-   -   1) The separation of substrate surface from the objective lens        is set within the focusing range.    -   2) To begin with, image is formed and captured by using        non-actinic illumination. This will not cause any damage to the        photo sensitive material for exposure. That is, the initial        focus is set by using non-actinic illumination; the objective is        then adjusted accordingly for best focus.    -   3) As the exposure stage starts to move along the direction of        substrate movement (the X direction), the actinic exposure        starts.    -   4) Image captured is then monitored under the actinic        illumination. The Objective lens is adjusted accordingly.    -   5) Note that each focus adjustment is for the next exposure site        but based on best focus determined for the previous exposure        location.    -   6) The amount of focus adjustment for the objective lens is        based on the optical path difference measured for f1 vs. f2.

As described above, the image writing may be monitored by one or morecameras on-the-fly while exposure is taking place. By using a mirrorpixel voting scheme for exposure, each image pattern is being exposedand formed by many DMD mirror pixels. This exposure scheme inherentlypermits more margin of focusing error at the initial stage of exposuresince each mirror pixel exposure only contributes a small fraction ofthe total exposure energy required. As pixel voting exposure progresses,the focus of each SLM imaging unit may be tuned and adjusted on-the-fly.This margin of focus error is important for writing the features thatare either isolated “hole-like” patterns surrounded by dark field, orisolated “island-like” patterns surrounded by a clear field such as theexample shown in FIG. 24. This is because both aforementioned featurepatterns are not easy to set optimum focus initially due to the lack ofimage variation while perturbing the focus setting. However, the optimumfocus can be determined after a number of exposures have beenprogressed.

In another approach, the type of auto-focusing mechanism described abovemay be used to accomplish “focus voting exposure” to expand the overallDOF. FIG. 25 illustrates a method for improving DOF through pixel votingexposures according to embodiments of the present invention. In theexample shown in FIG. 25, the optimum exposure setting can bedynamically tuned during the pixel voting exposure. This allows thepixel voting exposures to be accomplished by a different best focuslevels that are still within the DOF. This scheme enables the finalimage pattern to be exposed and formed by many votes of the focussettings 2502 that may extend to the overall resultant DOF 2504.

Embodiments of the present invention not only are applicable andbeneficial to the lithography for manufacturing of FPD and mask for FPDmanufacturing, the making of one-of-the-kind or precision duplicates oflife-sized art on glass substrate, they are also applicable andbeneficial to the manufacturing of integrated circuits, computergenerated holograms (CGH), printed circuit board (PCB), for largeimaging display applications in both micro and meso scales.

Embodiments of the present invention are further applicable andbeneficial to lithography manufacturing processes without using mask,such as writing intended mask data patterns to substrates directly. Inthis way, the mask cost and associated issues of concern are eliminated.Embodiments of the present invention enable exposure tools for mask-lessexposure that exceeds the throughput requirements for the upcoming G10and beyond. More importantly, this configuration comes with improvedprocess window to ensure better lithography yield.

It will be appreciated that the above description for clarity hasdescribed embodiments of the invention with reference to differentfunctional units and processors. However, it will be apparent that anysuitable distribution of functionality between different functionalunits or processors may be used without detracting from the invention.For example, functionality illustrated to be performed by separateprocessors or controllers may be performed by the same processors orcontrollers. Hence, references to specific functional units are to beseen as references to suitable means for providing the describedfunctionality rather than indicative of a strict logical or physicalstructure or organization.

The invention can be implemented in any suitable form, includinghardware, software, firmware, or any combination of these. The inventionmay optionally be implemented partly as computer software running on oneor more data processors and/or digital signal processors. The elementsand components of an embodiment of the invention may be physically,functionally, and logically implemented in any suitable way. Indeed, thefunctionality may be implemented in a single unit, in a plurality ofunits, or as part of other functional units. As such, the invention maybe implemented in a single unit or may be physically and functionallydistributed between different units and processors.

One skilled in the relevant art will recognize that many possiblemodifications and combinations of the disclosed embodiments may be used,while still employing the same basic underlying mechanisms andmethodologies. The foregoing description, for purposes of explanation,has been written with references to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Many modificationsand variations are possible in view of the above teachings. Theembodiments were chosen and described to explain the principles of theinvention and their practical applications, and to enable others skilledin the art to best utilize the invention and various embodiments withvarious modifications as suited to the particular use contemplated.

What is claimed is:
 1. A parallel imaging writer system, comprising: aplurality of spatial light modulator (SLM) imaging units, wherein eachof the plurality of SLM imaging units includes one or more illuminationsources, one or more alignment sources, one or more projection lenses,and a plurality of micro minors configured to project light from the oneor more illumination sources to the corresponding one or more projectionlens; and a controller configured to control the plurality of SLMimaging units, and the controller synchronizes movements of theplurality of SLM imaging units with movement of a substrate in writing amask data to the substrate in a lithography manufacturing process. 2.The parallel imaging writer system of claim 1, wherein the one or moreillumination sources include one or more actinic light sourcesconfigured to write a mask data pattern to the substrate, and the one ormore alignment sources include a non-actinic light source configured tofocus a SLM imaging unit to a corresponding area of the substrate. 3.The parallel imaging writer system of claim 2, wherein the non-actiniclight source includes a red laser diode and the one or more actiniclight sources include four blue laser diodes.
 4. The parallel imagingwriter system of claim 2, wherein the non-actinic light source includesa red light emitting diode (LED) and the one or more actinic lightsources include four blue LEDs.
 5. The parallel imaging writer system ofclaim 1, wherein the one or more projection lenses comprise: one or moreenlargement objective lenses.
 6. The parallel imaging writer system ofclaim 1, wherein the one or more projection lenses comprise: one or morereduction objective lenses.
 7. The parallel imaging writer system ofclaim 1, wherein each SLM imaging unit further comprises: a first camerasensor configured to observe defocus of the substrate on-the-fly.
 8. Theparallel imaging writer system of claim 7, wherein each SLM imaging unitfurther comprises: a first motor, a first refractive disk, and a firstoptical path difference (OPD) modifier, wherein the first camera sensor,the first motor, the first refractive disk, and the first OPD modifierare configured to adjust focus of the first camera sensor to thesubstrate on-the-fly.
 9. The parallel imaging writer system of claim 8,wherein each SLM imaging unit further comprises: a second camera sensor,wherein the first and second camera sensors are configured to observethe substrate with complementary focus offsets to determine direction ofa target focus.
 10. The parallel imaging writer system of claim 9,wherein each SLM imaging unit further comprises: a third OPD modifier,wherein the third OPD modifier is configured to adjust focus of the SLMimaging unit to the substrate on-the-fly without changing distancebetween the one or more projection lenses and the substrate.